Since the 1960's, diagnostic ultrasound has found wide application in all disciplines of medicine and particularly, in the reproductive sciences. Prior to conception, it is used to monitor follicular growth and development and subsequent ovulation. Once pregnancy is confirmed, in a vast majority of patients, the early human embryo is exposed to ultrasound for confirmation of fetal cardiac activity. Despite the non-ionizing character of ultrasound radiation and lack of proven adverse effects to humans, the assumption that ultrasonic energy levels currently employed in diagnostic instruments are without biohazard is not based on any direct experimental data with respect to the "actual" ultrasonic energy imparted to the ovary, early embryo and fetus during diagnostic ultrasound imaging. In-vivo and in- vitro investigations of the bioeffects of ultrasound, are difficult to extrapolate to humans because of the following reasons: often high energy levels are used to produce these bioeffects in non-clinical, experimental models; the effects of absorption and attenuation from the abdominal wall are not taken into account and the energy measured at the transducer face may be totally different from that measured at the organ of interest; the exposure time of the fetal organs is unknown; and the effect of ultrasonic beam focusing at various tissue depths is not considered. The specific aims of this proposal therefore are to measure the exact ultrasonic energy delivered to the human ovary, early embryo and mid-trimester fetus using currently available diagnostic imaging equipment. Specially designed hydrophones will be placed as close as possible to the ovaries in normal volunteers using a vaginal approach. Exposure to the embryo will be determined in patients undergoing first trimester spontaneous or voluntary abortions by placing the hydrophones as close as possible to the embryo in-utero prior to completion of the abortion. Mid-trimester fetal exposure will be determined using intrauterine placement of the hydrophone in patients undergoing voluntary abortion for obstetrical or genetic indications. Once the dosimetry in these clinical situations has been established, using direct experimental evidence we will test the hypotheses that (i) in vivo ultrasound exposure of the human ovary, embryo and fetus during a "routine" ultrasound examination is in fact several orders of magnitude less than the maximum ultrasound quantities measured in vitro (as has been postulated); and (ii) patient size and stage of gestation are directly related to the amount of ultrasound energy to which the ovary, embryo or fetus are exposed. Using these data we will be able to not only correctly estimate ultrasound exposure levels in any gynecologic or obstetrical ultrasound examination but also be able to experimentally test whether these levels of exposure can produce harmful effects.